Critical Win2K flaw yields multiple attack vectors

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Last week's very serious Windows 2000 vulnerability is far from limited to exploitation through IIS alone.

This flaw, the root cause of which is a buffer overflow vulnerability in a core Microsoft Windows DLL (ntdll.dll), could allow attackers to gain complete control of a vulnerable system and execute arbitrary code.

As we said in our article about a minor glitch with the patch last week, ISS WebDAV (World Wide Web Distributed Authoring and Versioning) is one of many Windows components which uses the problematic ntdll.dll component. So Microsoft's patch needs to be applied to all potentially vulnerable Windows 2000 boxes.

Microsoft's advice on the problem has been revised to take into account potential conflicts with hot fixes which gave rise to the minor glitch. This is just as well because the problem gets worse the closer you look at it.

David Litchfield, of NGSSoftware, the security firm which rose to prominence on the back of discovery of the vulnerability exploited by the Slammer worm, has dissected the myriad risks arising from the flaw. You can read his paper (PDF) here.

Along with malformed WebDAV requests to Microsoft's IIS 5 Web Server (which ships with Win2K) other attack vectors including Java-based Web servers and non-WebDAV related issues in IIS exist, NGSSoftware notes. And that's just the tip of a dangerous iceberg.

"Security researchers at NGSSoftware have already discovered several new attack vectors and believe that there will be many that come to light over the next few weeks," Litchfield writes.

"There are too many ways for an attacker to access the vulnerability. Likely areas will be non-MS Web and FTP servers, IMAP servers, anti-virus solutions and other MS Windows Services."

In light of this, NGSSoftware strongly advises that every Windows 2000 workstation and server needs to be patched - and patched soon - regardless of whether it is running IIS or not. ®